Proxy Re-Encryption-Based Traceability and Sharing Mechanism of the Power Material Data in Blockchain Environment

Abstract

The need to accelerate the innovation and application of the supply chain has been suggested by the State Council of China. To solve the problem of data isolation caused by privacy protection in the power material supply chain, a data traceability and sharing mechanism based on blockchain is designed in this paper. Firstly, the existing problems of the power material supply chain are introduced, and the applicability of blockchain in the power material supply chain in view of these problems is analyzed. Secondly, blockchain-based power material supply deployment and application structures are proposed. Then, considering the problem of data isolation in the material inspection and distribution links between suppliers and the material company, a data traceability mechanism based on blockchain is designed to provide evidence for the data authenticity and a proxy re-encryption method is used to ensure security and privacy in data sharing. Finally, the effectiveness of the proposed data traceability and sharing mechanism is verified using the Hyperledger Fabric platform for power material case studies. The simulation results show that the combination of proxy re-encryption and blockchain technology in the power material supply chain can confirm the validity of the historical data and keep the private data of the material company confidential, so as to realize the traceability and sharing of the power material supply data.

1. Introduction

With the development of modern information technology such as big data, cloud computing, Internet of Things (IoT), mobile Internet, artificial intelligence, and blockchain, the supply chain is facing new challenges and development opportunities. On the one hand, due to the rapid growth of data volume and the continuous improvement of data utilization requirements, higher requirements for the storage, processing, and sharing of information have been put forward by the modern smart supply chain. On the other hand, the application of modern information technology has achieved initial success, making the integration of the supply chain and modern information technology possible. In 2017, the necessity of accelerating the innovation and application of the supply chain and promoting supply-side structural reform was proposed by the State Council of China. As a decentralized distributed ledger technology, blockchain has authenticity, non-tampering, and traceability characteristics, which can meet the requirements of the supply chain for information storage and sharing.

Blockchain has been applied to different aspects of the power field, e.g., power trading [1,2], microgrid [3], smart grid [4], and demand response [5]. In terms of the supply chain, the opportunities and challenges that blockchain may face in the application process are analyzed in [6,7]. In [8], a supply chain framework based on blockchain technology is proposed, and the information tracking and multilateral cooperation among supply chain members are realized by using a distributed ledger and smart contract. The research on the global supply chain operation risk of aviation logistics is realized based on the combination of blockchain and the mean-variance method in [9]. The positive impact of blockchain in promoting cooperation and data sharing among supply chain participants is analyzed in [10,11]. The application focus of blockchain is shifted from traceability to supervision performance in [12], and a blockchain-based food supply chain credit evaluation system is proposed. In [13], the feasibility of blockchain technology towards the power material supply chain has been proved. The practical application of blockchain has also achieved initial success in the field of the supply chain. In 2017, a food safety alliance was jointly established by Walmart, International Business Machines Corporation (IBM), JD, and Tsinghua University to track the food supply chain by using blockchain. In 2018, a blockchain-based shipping and supply chain company was created by IBM and Maersk, which can digitize the end-to-end supply chain process based on Hyperledger Fabric, to improve the information transparency in the supply chain and achieve highly secure information sharing.

It can be seen that a suitable solution has not been provided by the existing research on blockchain to solve the problem of data isolation in the power material supply chain. The proxy re-encryption (PRE) algorithm realizes the data sharing by entrusting semi-trusted proxy to perform ciphertext conversion, which can be applied to solve the problem of data isolation. In [14], a PRE-based data-sharing scheme using blockchain nodes as trusted third parties is proposed to solve the privacy-protection problem caused by data sharing in cloud storage. The data security problems faced by vehicle communication data in the process of sharing are solved by combining PRE with smart contracts in [15].

Since there are various subjects involved in the inspection and distribution of the power material supply chain, and there are some private data that are not permitted to be disclosed to other subjects, it can represent the general problems existing in the power material supply chain. Therefore, the material inspection and distribution parts are taken as an example to study the application mode of blockchain and PRE technology in the power material supply chain, which can not only track and confirm the historical power material supply chain data but also realize the data sharing and keep the private data of the material company confidential. The novel contributions of the paper are introduced as follows:

• The power material supply deployment and application structures based on blockchain technology are established based on the applicability analysis of blockchain technology in the power material supply chain, which realizes the data exchange and business transmission between different units in the power material supply chain.
• The traceability and sharing mechanism of the power material data are designed based on the proxy re-encryption method and blockchain technology, which provides a meaningful reference for the problem of sharing private data on the blockchain.

The rest of the paper is structured as follows: In Section 2, the applicability of blockchain in the power material supply is analyzed based on the development reality of the power material supply chain. In Section 3, the blockchain-based structures of the power material supply are proposed. In Section 4, a data traceability mechanism and a proxy re-encryption method are designed to realize the credible data sharing in the inspection and distribution of the power material supply chain. The proposed data-sharing and traceability mechanism are simulated and verified on the Hyperledger Fabric platform in Section 5 and the conclusion in Section 6.

2. Power Material Supply Chain and Blockchain Technology

Supply chain, as a network structure formed by upstream or downstream companies, can provide products or services to users during the production and circulation process. Under the background of the continuous acceleration of supply chain innovation and application and the rapid development of modern information technology, the supply chain has developed into a new stage of smart supply chain deeply integrated with the Internet and IoT. For example, based on the actual demand and future development of the power material supply chain, a modern smart supply chain platform was built, as shown in Figure 1, by the State Grid Corporation of China. Intelligent procurement, digital logistics, and panoramic quality control have been realized on the platform by making full use of modern information technology, which promotes deep internal cross-professional collaboration and efficient external collaboration in the supply chain [16].

To simplify the database deployment structure and reduce the cost of data operation, a centralized data processing method has been adopted by the modern smart supply chain platform. However, the timeliness and reliability of the data interactions between suppliers, warehousing systems and logistics systems, and the supply chain platform have been greatly influenced by the centralized data processing method, which inevitably leads to a series of problems, such as a low efficiency of information flow, insufficient traceability of data and unguaranteed authenticity of information.

Taking State Grid Jiangsu Electric Power Company Material Branch in China as an example, the problems of the power material supply chain can be divided into the following three points: Firstly, the data exchange between suppliers and material companies may take even more than 5 days, which seriously affects the efficiency of the power material supply chain. Most of the information in the power material supply chain is physically isolated and difficult to exchange, which increases the need for manual operations. In terms of the overall data exchange of the power material supply chain, it is difficult for all entities to use the power material management platform system conveniently, which reduces the participation of all entities and cannot provide the original data and circulation channels for the data exchange of the supply chain. Additionally, the difficulty of information traceability is increased due to the high complexity of the power material information, various sources of the information, and the large period of the power material supply. Secondly, it often takes up to 4–6 months from the beginning of bidding to the effectiveness of the purchase agreement with strong uncertainty. The operation of the power material supply chain depends on the circulation of extensive contracts and documents due to the lack of informatization in some business links. Additionally, the processing of contracts and documents relies on logistics transshipment, and also requires a lot of manual approval and signatures due to the necessity of internal approval management, which makes the speed of the overall circulation slow. Thirdly, the risk of single-point failure in the information storage cannot be avoided absolutely because of the centralized information storage method. In addition, due to the design vulnerability of the management authority, the information in the power material platform system may also be tampered with, reducing the credibility of the information in the system.

Each node on the blockchain stores all transaction data in the chain and utilizes consensus mechanisms to ensure the consistency and authenticity of the data. In addition, technologies such as peer-to-peer network protocols, the asymmetric encryption algorithm, and smart contracts are also adopted in blockchain to realize the distributed application of blockchain in various fields. In order to demonstrate the practical significance of this paper in the power material supply and provide a basis for the data traceability and sharing mechanism in the following, the applicability of blockchain in the power material supply is analyzed based on the deficiencies of the existing material supply chain platform and the technical characteristics of blockchain in the following three aspects. In addition, the integrated applications of blockchain and the power material supply chain are also introduced, which can successfully solve the problems encountered in the existing power material supply chain [17].

• Data traceability and authenticity guarantee: Consensus mechanisms are used by the nodes to generate blocks with timestamps, which ensures the immutability and traceability of the data on the chain. The accurate traceability of the data in various links such as material processing and distribution is still difficult to achieve in the current material supply chain. Additionally, there is also the problem that the material inspection reports cannot be completely trusted by suppliers. Therefore, the power material supply can be combined with blockchain to realize the decentralized processing of the data in the supply chain. By storing the power material supply data recorded by suppliers, warehousing systems, and logistics systems on the blockchain through consensus mechanisms, the whole process of the material information can be traced back, which improves the interaction efficiency of information flow between the material company and suppliers and strengthens the interaction between different subjects in the power material supply chain.
• Process simplification: A smart contract on the blockchain is a computer transaction protocol with the characteristics of being intermediary free, self-verification, and automatic execution. Based on the trusted and tamper-proof data on blockchain, the pre-defined rules and terms can be automatically implemented by the smart contract to realize the efficiency and irreversibility of transactions. At present, there are still many cumbersome and complicated procedures in the power material supply chain that require offline executions and layered approvals, which greatly reduce the efficiency of information flow and business execution. The business process can be stored by the smart contract on the blockchain in the form of contract terms. Additionally, the relevant procedures can be automatically executed by calling the corresponding smart contract, which reduces the consumption of human and material resources, the uncertainty in the business process, and improves the business execution efficiency on the power material supply chain. Moreover, the smart contract is deployed on the blockchain, which realizes its openness, transparency, and traceability in the process of deployment, invocation, and execution, and ensures the legal compliance of procedures in the power material supply.
• Protection of data privacy and system security: Asymmetric encryption, used in the blockchain to ensure data privacy, uses a public key and private key to encrypt and verify the data on the blockchain, which can ensure the confidentiality of the transactions on the blockchain. At present, there is still a large vacancy in the application of cryptography algorithms in the power material smart supply chain. Therefore, asymmetric encryption algorithms can be used to avoid the risk of privacy disclosure caused by the single point failure or the design vulnerability of management authority in multiple links such as demand declaration, bidding, procurement, inspection, and distribution.

3. Structure of the Power Material Supply Chain Based on Blockchain

At present, more comprehensive and specific requirements are put forward to improve the automation of the power material supply process and reduce the security risk of the power material supply information, which accelerates the innovation and development of the power material supply chain. The combination of blockchain and the power material supply chain, as mentioned above, can not only ensure the data privacy of different supply chain entities through asymmetric encryption technology but also simplify the supply chain business process and realize the traceability of data on the chain by using a smart contract. Therefore, a power material deployment structure and application structure based on blockchain are proposed in this section, which provides a channel for data exchange and business management between different entities in the power material supply chain.

Considering the requirements of data interaction between different subjects on the power material supply chain and the modern smart supply chain platform, the power material supply deployment structure is built with the consortium blockchain in this paper, as shown in Figure 2 [18]. The warehousing system, logistics system, financial institution, and suppliers of power material supply chain are selected as the nodes on the blockchain to participate in the data interaction and consensus in the process of power material supply. As the subnodes of the State Grid node, each business platform participates in the consensus process on the chain and realizes the data exchange with multiple nodes on the blockchain [19].

The data center in the power material supply chain is replaced by the application of blockchain, which can not only realize the storage and traceability of normalized business data but also complete the reception and forwarding of time-sensitive business data based on the distributed ledger. For the front-end application of the power material supply chain, the generation of real-time business data and feedback of business links can also be accomplished by the blockchain, which ameliorates the method of data generation and the speed of data feedback with the front-end function of the power material supply chain being immutable. As a node in the consortium blockchain, the enterprise supply chain center (ESC) can accelerate the transmission efficiency of business instructions based on real-time data sharing on the blockchain. Moreover, the smart contract on the blockchain can also be used by the ESC to execute relevant business processes, which can avoid the complex steps of offline execution and realize the automatic promotion of the whole process of the power material supply business [20].

For each participant of the power material supply chain, access to the blockchain means that the data can be put on the chain in real time, and the authenticity and effectiveness of the data are verified jointly. Therefore, the reliability of the quality information, logistics information, and storage information in the power material supply chain is guaranteed, and the problems of information inequality and data lag in the power material supply chain are solved.

To realize the application of blockchain in the field of the power material supply chain, a blockchain-based application structure of the power material supply chain is constructed, as shown in Figure 3. The structure mainly includes five parts, the subject of responsibility, channel layer, application layer, service layer, and data layer, which will be introduced in the following section.

• The subject of responsibility in the power material supply chain: There are frequent and complex information interactions among the subjects in the power material supply chain, such as the material company, suppliers, testing organization, and judiciary. Therefore, on the power material supply consortium blockchain, the control and management of nodes and transaction data are usually completed by multiple responsible subjects, which not only ensures the data on the chain are non-tampering, but also reduces the operation cost of the blockchain.
• The channel layer for information interaction: As the main support for external data access and data circulation, the channel layer, with intranet PC, extranet PC, mobile APP, a large screen display, and data interface included, can realize data exchange between different business platforms and between three-party units and the material company. Among them, the intranet PC can realize the data access of various departments in the power material company on the blockchain and provide channels for data interaction between multiple management platforms. The external PC is applied to provide data interfaces connected to the blockchain for suppliers, testing organization, supervision company, and judiciary. Additionally, the mobile app can provide convenient operation and management methods for handheld applications. Additionally, the data interface is designed to summarize the various information in the data layer for blockchain services and integrated support services.
• Application layer for function design: The application layer mainly includes six modules: electricity logistics services platform, enterprise resource planning, handheld application, e-commercial platform, enterprise supply chain center, and electrical equipment intelligent IoT platform, which can realize the application mode design and function customization of blockchain in the power material supply chain. After receiving the instructions from the power material company or other entities in the power material supply chain, the application layer will use different blockchain services or integrated support services according to the preset process, and the results obtained after the program execution will be fed back to the user.
• Service layer for supporting various applications. Through the hash pointer and consensus mechanism, all transaction information is stored in the database of each participating node in a chain structure by the blockchain service. Additionally, the transactions on the blockchain are also executed by the blockchain service according to the preset logic through the smart contract composed of an automatic script code, which realizes the trust-free, traceability, and non-tampering characteristics of data. An integration support service is an auxiliary service necessary for business integrity and process automation, and is paperless, which provides the services and functions required for the normal operation of the structure together with the blockchain service. The service layer receives instructions from the application layer, obtains real-time data from the data layer, and executes specific services according to requirements, and then the execution results will be fed back to the service layer.
• The data layer for dealing with power material data and blockchain data: With business data, contract data, monitoring data, cross-chain data included, the data layer is the basis for the operation of the blockchain and the realization of various application services, which can be used to meet various data requirements of the service layer.

Through the connection between the channel layer, application layer, service layer, and data layer in the blockchain-based application structure, the integration of business information and management methods and the requirements for data traceability and reliability in the power material supply chain are realized.

As mentioned above, the existing modern smart power supply chain platform still has deficiencies in data traceability and authenticity, process simplification, and the protection of data privacy and system security. Therefore, blockchain is applied to solve the deficiencies above. However, the research of blockchain technology applied in the field of power material supply chain mostly focuses on the theoretical stages such as prospect, application, and management analysis, lacking visual structure support. In addition, the blockchain structure applied in other fields cannot be perfectly integrated with the power material supply chain. Therefore, this paper combines blockchain technology with the power material supply chain and designs the deployment architecture and application architecture of the power material supply chain based on blockchain technology, which can enhance the privacy of node data, simplify the business process, and realize the traceability of the power material supply data compared with the existing power material supply technology. Additionally, the deployment structure and application structure constructed in this paper have taken the suppliers, logistics, warehousing, finance, and other units involved in the process of the power material supply into consideration compared with the existing application research of blockchain technology. The structures can not only meet the different application needs of the power material supply chain but also provide relevant services for data exchange with external and cross chains.

4. Traceability and Sharing Mechanism of the Power Material Data Based on PRE in the Blockchain Environment

4.1. Preliminary Definitions of Blockchain and PRE

Blockchain is a distributed public ledger jointly maintained by the nodes of the whole network in a decentralized manner. Each node on the blockchain stores all the information of the whole blockchain, which is jointly managed, maintained, and supervised by all nodes of the blockchain. Additionally, each block on the blockchain saves the latest transaction data and the hash value of the previous block, which can be used to ensure the connection between blocks. Therefore, any change to the data will greatly change the hash value, so as to ensure the non-tampering and traceability of the data on the chain. Blockchain is a decentralized network without any authoritative third party to supervise and control it, which completes the corresponding functions through technologies such as consensus mechanisms, asymmetric encryption, and smart contracts. A consensus mechanism can ensure the consistency of data stored by different nodes on the blockchain, asymmetric encryption can be used to protect the private data of the nodes, and a smart contract is equivalent to a computable transaction protocol that implements the terms of the contract.

Proxy re-encryption is a concept proposed by Blaze et al. in 1998 [21]. The PRE entrusts a semi-trusted proxy to convert the ciphertext encrypted by A into ciphertext decryptable for B [22]. In this process, any plaintext information cannot be obtained by the semi-trusted proxy other than B, which can realize data sharing under the condition of ensuring privacy. Proxy re-encryption can take many forms, which can be divided into unidirectional proxy re-encryption and bidirectional proxy re-encryption according to the different directions of ciphertext conversion. Additionally, according to the different times of re-encryption key conversion, PRE can be divided into single-hop ciphertext conversion and multi-hop ciphertext conversion. The proxy re-encryption scheme based on the single-hop and unidirectional is applied in this paper, which includes the following algorithms:

• Key generation algorithm: $KeyGen\left(par\right)\to \left(pk,sk\right)$. Input the system public parameter par, and the algorithm will output (pk, sk) as a user’s public–private key pair.
• Encryption algorithm: $Encrypt\left(par,m,p{k}_i\right)\to C_i$. Input the system public parameter par, plaintext m, and the delegator’s public key pk_i, the algorithm will output the ciphertext C_i encrypted by the public key pk_i.
• Conversion key generation algorithm: $ReKeyGen\left(par,s{k}_i,p{k}_j\right)\to r{k}_{i\to j}$. Input the private key sk_i of the delegator and the public key pk_j of the delegatee, the algorithm will output the conversion key rk_i→j, which is used for one-way re-encryption from delegator to delegate.
• Re-encryption algorithm: $ReEncrypt\left(r{k}_{i\to j},C_i\right)\to C_j$. Input the proxy re-encryption key rk_i→j and the delegator’s ciphertext, and the proxy re-encryption algorithm will output the re-encrypted ciphertext C_j for the delegate.
• Decryption algorithm: $Decryt\left(par,s{k}_j,C_j\right)\to m$. Input the delegate’s private key sk_j and the ciphertext C_j corresponding to the delegate, and the algorithm will output the corresponding plaintext m.

The algorithm of the proxy re-encryption scheme also needs to meet the consistency, which means that the following equation should be met for any set of public parameters par, any plaintext m, and any user public–private key pair (pk, sk):

$$Decryt\left(par,s{k}_i,Encrypt\left(par,m,p{k}_i\right)\right)=m$$

(1)

$$Decryt\left(par,s{k}_j,ReEncrypt\left(ReKeyGen\left(par,s{k}_i,p{k}_j\right),C_i\right)\right)=m$$

(2)

4.2. Power Material Data Traceability and Sharing Mechanism

The application of blockchain technology in the power material supply chain mainly focuses on the guarantee of the security, authenticity, and traceability of material information, the flow efficiency of material data on the supply chain, and the intelligent management of business data. As an important business link in the supply chain, power material inspection and distribution involve many subjects, such as the material company, testing organizations, material suppliers, and logistics units. Moreover, there are many information interactions between various subjects, including the original, process, and result information of all links from the standardized intelligent management of warehousing, visual testing to smart material distribution. Therefore, problems such as data loss or data damage are prone to occurring when circulating between different subjects. At present, the storage, inspection, and distribution information of the power material supply chain is mainly stored in the centralized database by manual input, whose reliability and confidentiality cannot be guaranteed. How to realize the efficient allocation of physical resources through the feedback of information system will be the most critical theme in the future [23].

Taking the power material supply chain of the State Grid Corporation of China as an example, the existing material inspection and distribution link are mainly composed of suppliers, warehouses, and inspection organizations of the power material supply chain. Additionally, the data of each link on the supply chain need to be stored in the power material smart supply chain platform and uniformly dispatched by the operation center, which realizes the intellectualization of material inspection and distribution to a certain extent. However, there are still some deficiencies in the existing technology in realizing the traceability of the power material information, which undoubtedly brings many problems to the whole life cycle management of the power material supply. In addition, when the suppliers disagree with the material quality inspection data, effective supporting proof needs to be provided by the material company to the suppliers. However, as the core business information of the material company, the sampling plan, for example, cannot be directly disclosed to suppliers to prevent improper collusion between suppliers and testing organizations. In this case, suppliers find it difficult to trust the inspection quality data provided by the material company, which is not conducive to building an honest and fair competitive environment on the power material supply chain [24].

Considering the characteristics of blockchain in ensuring the authenticity, reliability, and traceability of data, which can resolve the problems of insufficient reliability and lacking traceability of the data in the inspection and distribution links of the existing power material supply chain, a data traceability mechanism for inspection and distribution links of power material based on blockchain is proposed, as shown in Figure 4. Suppliers, material warehouses, and inspection organizations are not only the uploaders of the power material business, data but also the participants of the consensus process on the consortium blockchain, which ensures the authenticity and reliability of the logistics and quality inspection data stored on the blockchain [25,26].

The data block on the blockchain is generally composed of a block header and block body. All transaction information on the block is mainly contained in the block body and the hash value of the transaction information in the block body can be expressed as

$$H_i=f_{SHA256}\left(T_i^r\right),i=1,2,\cdots ,n$$

(3)

$$H_{xy}=f_{SHA256}\left(H_x,H_y\right),\left(x,y\right)=\left(1,2\right),\left(3,4\right),\cdots ,\left(n-1,n\right)$$

(4)

where $T_i^r$ represents the transaction information stored in the block; $f_{SHA256}$ is the hash function of SHA256; $H_i$ denotes the hash value of $T_i^r$; n represents the number of transactions stored in the block.

The block header contains the hash value of the current block, which can be expressed as

$$H_c=f_{SHA256}\left(N_r,T_s,M_r,B_n,H_p\right)$$

(5)

where $N_r$ is a random number; $T_s$ denotes the timestamp of the current block; $M_r$ represents the Merkle tree root of the transaction information stored in the block; $B_n$ is the number of the current block; $H_p$ denotes the hash value of the previous block; and $H_c$ represents the hash value of the current block.

In Figure 4, all blocks on the blockchain are linked into a complete one-way chain in chronological order, which can be represented as:

$$\begin{array}{l}{H_c}^{″}=f_{SHA256}\left(\cdots ,{H_p}^{″}\right)=f_{SHA256}\left(\cdots ,H_c\right)\\ =f_{SHA256}\left(\cdots ,f_{SHA256}\left(\cdots ,H_p\right)\right)=f_{SHA256}\left(\cdots ,f_{SHA256}\left(\cdots ,{H_c}^{\prime }\right)\right)\end{array}$$

(6)

where ${H_c}^{″}$ is the hash value of the latter block; ${H_c}^{\prime }$ is the hash value of the previous block; and ${H_p}^{″}$ denotes the hash value of the current block, which equals to $H_c$.

Therefore, all the information stored on the blockchain can be traced back. For material processing, quality inspection, and logistics information in the power material supply chain, a one-way chain with a traceable source and searchable purpose can be formed according to the timestamps of material arrival, inspection, and distribution. Thus, querying logistics information in real time and tracking the source of the power material can be accomplished by the one-way chain for the material company and other participants of the power material supply chain.

The quality report stored on the blockchain contains quality data, quality inspection results, the name of the testing organization, and other inspection data. Some of these data are private data within the material company and cannot be disclosed to the public, and need to be asymmetrically encrypted with public key. These data are stored in the form of ciphertext on the blockchain and can be decrypted only by the corresponding private key, which means that the quality inspection information of the power material is invisible to any other subjects except the material company. In other words, any effective information cannot be obtained through the ciphertext of the quality inspection information, which effectively ensures the privacy and security of the inspection data [27]. At the same time, it is impossible for material suppliers who need to verify the authenticity and reliability of the quality inspection information to obtain reliable data from the blockchain. Therefore, the key to the problem is how to share the quality inspection data without divulging the privacy of the material company and ensure the authenticity of the data in the meanwhile.

A power material privacy data-sharing method based on PRE is designed in this paper, as shown in Figure 5, which is mainly composed of the following six links [28]:

1.

Initialization of public parameter: $Setup\left(1^k\right)\to par$

After inputting the safety parameter k, a bilinear mapping is output, which is recorded as $\left(q,g,\mathbb{G},{\mathbb{G}}_T,e\right)$, where q is the order of the cyclic groups $\mathbb{G}$ and ${\mathbb{G}}_T$. e represents the mapping $e:\mathbb{G}\times \mathbb{G}\to {\mathbb{G}}_T$ and $g\stackrel{R}{\in }\mathbb{G}$ is a generator in $\mathbb{G}$. At the same time, $H:{\left\{0,1\right\}}^{*}\to {\mathbb{Z}}_q^{*}$ represents a one-way and anti-collision hash function in cryptography and can map binary strings of any length to ${\mathbb{Z}}_q^{*}$, which can be instantiated with SHA-256. $g_1,h_1,h_2,h_3,h_4$ are generators in $\mathbb{G}$ different from the g and the public parameter par, which can be expressed as:

$$par=\left\{g,\mathbb{G},{\mathbb{G}}_T,e,g_1,h_1,h_2,h_3,h_4,H\right\}$$

(7)

2.

Generation of the public key and private key: $KeyGen\left(par\right)\to \left(p{k}_i,s{k}_i\right)$

$p{k}_A=g^{x_A}$ and $s{k}_A=x_A$ are the public key and private key of the power material company A, respectively; $p{k}_B=g^{x_B}$ and $s{k}_B=x_B$ are the public key and private key of the supplier B, respectively, which can be obtained after the input of the public parameter par and the random selection of $x_A,x_B\stackrel{R}{\in }{\mathbb{Z}}_q^{*}$.

3.

Quality inspection data encryption and upchain: $Encrypt\left(par,m,p{k}_A\right)\to C_A$

To encrypt the quality inspection data m based on the public key $p{k}_A$ of the material company A and generate the quality inspection data ciphertext $C_A$, it is necessary to randomly select $r\stackrel{R}{\in }{\mathbb{Z}}_q^{*}$ and calculate:

$$C_A^1=g^r$$

(8)

$$C_A^2=m\cdot e{\left(g_1,p{k}_A\right)}^r$$

(9)

$$C_A^3={\left(h_1^{H\left(C_A^1\right)}{h}_2^{H\left(C_A^1\parallel C_A^2\right)}{h}_3\right)}^r$$

(10)

where $C_A^1$, $C_A^2$ and $C_A^3$ are the elements of the quality inspection data ciphertext $C_A$. Finally, the ciphertext is represented as:

$$C_A=\left(C_A^1,C_A^2,C_A^3\right)$$

(11)

4.

Calculation of conversion key: $ReKeyGen\left(par,s{k}_A,p{k}_B\right)\to r{k}_{A\to B}$

Transmit the public parameter par, the private key $s{k}_A$ of the material company A and the public key $p{k}_B$ of the material supplier B to a semi-trusted proxy, and the conversion key $r{k}_{A\to B}$ can be expressed as:

$$r{k}_{A\to B}=\left(r{k}_1,r{k}_2,r{k}_3,r{k}_4\right)$$

(12)

$$r{k}_1=g^k$$

(13)

$$r{k}_2=g_1^{-s{k}_A}p{k}_B^k$$

(14)

$$r{k}_3=e{\left(p{k}_B,p{k}_B\right)}^k$$

(15)

$$r{k}_4={\left(h_2^{H\left(r{k}_1\parallel r{k}_2\parallel r{k}_3\right)}{h}_4\right)}^k$$

(16)

where $k\stackrel{R}{\in }{\mathbb{Z}}_q^{*}$ is randomly selected, and $r{k}_1$, $r{k}_2$, $r{k}_3$ and $r{k}_4$ are the elements of the conversion key $r{k}_{A\to B}$.

5.

Re-encrypted ciphertext calculation: $ReEncrypt\left(r{k}_{A\to B},C_A\right)\to C_B$

The ciphertext $C_A$ is re-encrypted by the semi-trusted proxy to obtain the re-encrypted ciphertext $C_B$, which is represented as:

$$C_B=\left(C_B^1,C_B^2,C_B^3,C_B^{1^{\prime }},C_B^{2^{\prime }},C_B^{3^{\prime }}\right)$$

(17)

$$C_B^1=C_A^1$$

(18)

$$C_B^2=C_A^2\cdot e\left(C_A^1,r{k}_2\right)$$

(19)

$$C_B^3=C_A^3$$

(20)

$$C_B^{1^{\prime }}=r{k}_1$$

(21)

$$C_B^{2^{\prime }}=r{k}_1^{s{k}_A}$$

(22)

$$C_B^{3^{\prime }}={\left(h_1^{H\left(C_B^1\parallel C_B^2\parallel C_B^3\parallel C_B^{1^{\prime }}\parallel C_B^{2^{\prime }}\right)}{h}_2\right)}^{H\left(r{k}_3^{s{k}_A}\right)}$$

(23)

where $C_B^1$, $C_B^2$, $C_B^3$, $C_B^{1^{\prime }}$, $C_B^{2^{\prime }}$ and $C_B^{3^{\prime }}$ are the elements of the re-encrypted ciphertext $C_B$.

6.

Decryption of the re-encrypted ciphertext: $Decryt\left(par,s{k}_B,C_B\right)\to m$

Verify whether the equation

$$e\left(g^{H\left(e{\left(C_B^{2^{\prime }},p{k}_B\right)}^{s{k}_B}\right)},h_1^{H\left(C_B^1\parallel C_B^2\parallel C_B^3\parallel C_B^{1^{\prime }}\parallel C_B^{2^{\prime }}\right)}{h}_2\right)=e\left(g,C_B^{3^{\prime }}\right)$$

(24)

is valid. If so, the quality inspection data m can be recovered through the following calculation:

$$m=\frac{C_B^2}{e{\left(C_B^1,C_B^{1^{\prime }}\right)}^{s{k}_B}}$$

(25)

In this process, the quality information obtained by suppliers comes from the blockchain, which ensures the authenticity and non-tampering characteristics of the data. At the same time, the plaintext information of data cannot be obtained by other unrelated suppliers, which realizes the data sharing of the specific supplier [29].

5. Case Study

To verify the traceability of the power material data on the blockchain and the effectiveness of the proposed power material privacy data sharing method based on PRE, the case study was simulated in Windows 10, with the processor of Intel(R) Core(TM) i5-9400F CPU @ 2.90 GHz, and the simulation of the power material data traceability and privacy was conducted using Hyperledger Fabric 2.4.

5.1. Hyperledger Fabric Platform

As one of the mainstream open-source platforms of the consortium chain, Hyperledger Fabric provides a permissioned blockchain for application scenarios of enterprise level. Hyperledger Fabric can solve the trust problem among multiple weak trust enterprises, reduce the trust cost caused by complex and cumbersome business processes, and effectively improve the efficiency of large-scale collaborative activities among enterprises.

Based on the Hyperledger Fabric platform, the power material supply consortium blockchain test system was designed as shown in Figure 6, which can meet the simulation requirements for data management in the power material supply chain. The designed test system mainly includes 5 organizations, 11 nodes, and 2 channels. Among them, the five organizations, consisting of the energy bureau, State Grid Jiangsu electricity power company, State Grid Beijing electricity power company, Nanjing automatic research institute, and industrial and commercial banks of China, realize the control of access rights and user registration by issuing digital certificates. The two channels can be divided into the power channel for dealing with transactions of power and energy and the material channel for power material supply chain business. Additionally, the 11 nodes can be divided into two types. The first type is the orderer node completing the consensus work in the blockchain, and the other type is the peer node joining the channel and saving a copy of the ledger data in the channel.

5.2. Traceability Mechanism of Power Material Supply Data Based on Hyperledger Fabric

Taking the quality inspection and logistics process of transformers as an example, the simulation is carried out on the single machine test system of the power material supply blockchain based on Hyperledger Fabric, so as to verify the applicability of blockchain in the power material inspection and the function of blockchain in ensuring data credibility and process traceability, as shown in Figure 7.

The uploading of the quality inspection and logistics information is mainly accomplished by the material company, supplier, testing organization, and logistics company, respectively, so as to form a one-way chain connected by the blockchain structure to trace the data on the chain. The material ID of different batches of the power material is unique, which means that the material company can query the corresponding logistics information on the blockchain according to the material ID. The logistics information of the power material supply chain within one month provided by State Grid Jiangsu Electric Power Company Material Branch in China is taken as an example of the simulation. The generation time of each block in the blockchain is about ten seconds. In order to facilitate the simulation research, two hours in real time is equivalent to ten seconds in the simulation, and the result is shown in Figure 7. The status of the power material underwent two changes, from arrival and warehousing to inspection and from inspection to the upchain of quality inspection data. The status information of the power material is stored in blocks with the numbers of 94, 106, and 153, and is sequenced by the timestamps. When suppliers doubt the authenticity of the power material quality inspection data, corresponding applications can be submitted to the material company to query the status of the power material quality inspection data on the blockchain. Therefore, the hash value of the previous block on the blockchain with the current state of the power material stored can be used to trace the power material quality inspection data by the material company, which can ensure the authenticity and reliability of the data traceability process. Additionally, the obtained quality inspection data can be shared with the suppliers by the PRE, so as to ensure the privacy of the material company and the effectiveness of the quality inspection data [30].

5.3. Power Material Data Sharing Mechanism Based on PRE

To verify the effect of the proposed PRE mechanism in the process of the power material quality inspection data sharing, a power material data-sharing mechanism based on PRE is designed in six steps, as shown in Figure 8.

When the supplier has doubts about the quality inspection results of the power material, the PRE is used by the material company to provide real and reliable quality inspection information for the supplier with the private data of the material company protected. In the initialization of public parameter stage, the random generators are selected and the public parameter par is calculated by the company A, which will be exposed to the supplier B and the semi-trusted proxy. Then, the public key $p{k}_A=83e5\dots f74c$ and the private key $s{k}_A=25cd\dots 4212$ of the material company A will be sent to the semi-trusted proxy together with the public key $p{k}_B=3614\dots 57ab$ and the private key $s{k}_B=2496\dots 22f1$ of the material supplier B in the stage of generation of public key and private key. Additionally, the public key $p{k}_i$ and private key $s{k}_i$ of the material company A and the supplier B in the power material supply consortium blockchain can be used to verify the authenticity of the identity and data on the blockchain. In the stage of quality inspection data encryption and upchain, the quality inspection data such as material name, inspection conclusion, and inspector are encoded into corresponding data $m=bba5\dots 3944$. Additionally, the ciphertext $C_A$, stored on the blockchain for the semi-trusted proxy and material supplier to query, is generated using the public key $p{k}_A$ to encrypt the quality inspection data $m$ by material company A. In the calculation of the conversion key stage, the semi-trusted proxy will obtain the re-encrypted key $r{k}_{A\to B}$ by executing the key conversion algorithm according to the public parameter par, the private key $s{k}_A$ of material company A and the public key $p{k}_B$ of material supplier B. Then, the semi-trusted proxy will re-encrypt the encrypted ciphertext $C_A$ with the re-encryption key $r{k}_{A\to B}$ to obtain the re-encrypted ciphertext $C_B$ and send it to material supplier B in the re-encrypted ciphertext calculation stage. In the final stage of the decryption of the re-encrypted ciphertext, the effectiveness of the re-encrypted ciphertext $C_B$ will be verified first according to the system public parameter par and the private key $s{k}_B$ of material supplier B. If the verification is successful, the quality inspection data m can be calculated according to the corresponding algorithm, which guarantees the authenticity and effectiveness of the data. Additionally, the data m can also be decoded into the original quality inspection data with the material name, inspection conclusion, and inspector inside.

For suppliers or malicious attackers on the network who have obtained the re-encrypted ciphertext $C_B$ through improper means, the correct power material quality inspection data cannot be obtained with the re-encrypted ciphertext $C_B$ alone. In the re-encrypted ciphertext calculation stage, the re-encrypted ciphertext $C_B$, calculated according to the ciphertext $C_A$ and the re-encrypted key $r{k}_{A\to B}$, which can be obtained by executing the key conversion algorithm according to the public parameter par, the private key $s{k}_A$ of material company A and the public key $p{k}_B$ of material supplier, may be exposed to other suppliers or malicious attackers on the network due to network security problems. In the final stage of decryption of the re-encrypted ciphertext, although the public parameter par is known to all the nodes on the blockchain, the accuracy and authenticity of the re-encrypted ciphertext $C_B$ cannot be verified with the absence of the private key $s{k}_B$, and it is also difficult to obtain the correct power material quality inspection data m.

The smart contract in the blockchain, with the algorithm logic of the PRE written inside, can be used as a semi-trusted proxy. When it is necessary to share the power material data, the PRE is automatically executed by calling the relevant smart contract, so as to avoid the possible risk of data leakage caused by the semi-trusted proxy, and further improve the efficiency and reliability of the data sharing in the power material supply chain.

In this section, the simulation of the proposed traceability and sharing mechanism of the power material data on Hyperledger Fabric is accomplished. The simulation shows that the PRE method and blockchain technology applied for realizing the traceability and sharing of the power material data are effective.

6. Conclusions

In this paper, the application mode of blockchain in the field of power material sup-ply is studied. Based on the analysis of the applicability of blockchain, the deployment structure and application structure of the power material supply chain based on blockchain were constructed. Considering the problem of data tracing and isolation in power material inspection and distribution, a data traceability and sharing mechanism based on PRE is proposed, and the effectiveness of the proposed mechanism is verified on the Hyperledger Fabric platform. The practical effect of the proposed solution to solve the problem of data isolation can be summarized as the following points:

• The blockchain-based power material supply deployment and application structures meet the different application needs of the power material supply chain and provide relevant services for data exchange with external and cross chains.
• The data traceability mechanism based on blockchain can track the historical power material supply chain data and confirm the authenticity of the data.
• The combination of proxy re-encryption and blockchain technology in the power material supply chain can realize the data sharing and keep the private data of the mate-rial company confidential. Additionally, the corresponding power material supply data cannot be obtained by the supplier without the conversion key, which requires the permission of the material company.

Nowadays, the research of blockchain in the power material supply chain is increasing, and the data traceability and sharing mechanism proposed in this work is committed to providing a reference for the practical application of blockchain in the supply chain of China. Future research should be focused on the further integration and application of blockchain technology and the power material supply chain, as well as the combination of innovative proxy re-encryption methods and various blockchain projects.